My understanding of a table is when there is a data in a column, it is shown vertically with a number of rows.

I want to display the data in horizontal way separated by a comma.. So say my query returns me 12 rows, so instead of having 1 column and 12 rows, I want the data to be displayed in one single row each separated by a comma or similar..

You could do this with a crosstab or just hide or delete the table detail row and add an aggregation element to the table footer and use the CONCATENATE function. See attached report for an example of both approaches.